AIM2 inflammasome contributes to brain injury and chronic post-stroke cognitive impairment in mice
https://www.nature.com/articles/s41419-020-2248-z
- Article
- Open Access
- Published:
Inhibition
of AIM2 inflammasome activation alleviates GSDMD-induced pyroptosis in
early brain injury after subarachnoid haemorrhage
Cell Death & Disease
volume 11, Article number: 76 (2020)
Abstract
Only
a few types of inflammasomes have been described in central nervous
system cells. Among these, the absent in melanoma 2 (AIM2) inflammasome
is primarily found in neurons, is highly specific and can be activated
only by double-stranded DNA. Although it has been demonstrated that the
AIM2 inflammasome is activated by poly(deoxyadenylic-deoxythymidylic)
acid sodium salt and leads to pyroptotic neuronal cell death, the role
of AIM2 inflammasome-mediated pyroptosis in early brain injury (EBI)
after subarachnoid haemorrhage (SAH) has rarely been studied. Thus, we
designed this study to explore the mechanism of gasdermin
D(GSDMD)-induced pyroptosis mediated by the AIM2 inflammasome in EBI
after SAH. The level of AIM2 from the cerebrospinal fluid (CSF) of
patients with SAH was detected. The pathway of AIM2
inflammasome-mediated pyroptosis, the AIM2/Caspase-1/GSDMD pathway, was
explored after experimental SAH in vivo and in primary cortical neurons
stimulated by oxyhaemoglobin (oxyHb) in vitro. Then, we evaluated
GSDMD-induced pyroptosis mediated by the AIM2 inflammasome in AIM2 and
caspase-1- deficient mice and primary cortical neurons generated through
lentivirus (LV) knockdown. Compared with that of the control samples,
the AIM2 level in the CSF of the patients with SAH was significantly
increased. Pyroptosis-associated proteins mediated by the AIM2
inflammasome were significantly increased in vivo and in vitro following
experimentally induced SAH. After AIM2 and caspase-1 were knocked down
by an LV, GSDMD-induced pyroptosis mediated by the AIM2 inflammasome was
alleviated in EBI after SAH. Intriguingly, when caspase-1 was knocked
down, apoptosis was significantly suppressed via impeding the activation
of caspase-3. GSDMD-induced pyroptosis mediated by the AIM2
inflammasome may be involved in EBI following SAH. The inhibition of
AIM2 inflammasome activation caused by knocking down AIM2 and caspase-1
alleviates GSDMD-induced pyroptosis in EBI after SAH...
In recent years, an increased number of studies have indicated that inflammasomes are involved in EBI following SAH. Although many inflammasomes have been identified, only a few have been described and characterised in the central nervous system (CNS)4. Absent in melanoma 2 (AIM2), a member of the haemopoietic interferon-inducible nuclear 200 family of proteins, induces the formation of a highly specific type of inflammasome in the neurons that can recognise aberrant double-stranded DNA (dsDNA). AIM2 triggers the formation of inflammasomes that also contain the apoptosis-associated speck-like protein containing a CARD (ASC) and caspase-1 and that induce the cleavage of caspase-1, the maturation of interleukin-1β (IL-1β) and interleukin-18 (IL-18) and pyroptosis. The AIM2 inflammasome mediates pyroptotic neuronal cell death, as has been shown in vivo by incubating cortical neurons with poly(deoxyadenylic-deoxythymidylic) acid sodium salt, a synthetic dsDNA5. However, the role of gasdermin D (GSDMD)-induced pyroptosis mediated by the AIM2 inflammasome in the pathogenesis of EBI after SAH has not been clearly elucidated.
In recent years, an increased number of studies have indicated that inflammasomes are involved in EBI following SAH. Although many inflammasomes have been identified, only a few have been described and characterised in the central nervous system (CNS)4. Absent in melanoma 2 (AIM2), a member of the haemopoietic interferon-inducible nuclear 200 family of proteins, induces the formation of a highly specific type of inflammasome in the neurons that can recognise aberrant double-stranded DNA (dsDNA). AIM2 triggers the formation of inflammasomes that also contain the apoptosis-associated speck-like protein containing a CARD (ASC) and caspase-1 and that induce the cleavage of caspase-1, the maturation of interleukin-1β (IL-1β) and interleukin-18 (IL-18) and pyroptosis. The AIM2 inflammasome mediates pyroptotic neuronal cell death, as has been shown in vivo by incubating cortical neurons with poly(deoxyadenylic-deoxythymidylic) acid sodium salt, a synthetic dsDNA5. However, the role of gasdermin D (GSDMD)-induced pyroptosis mediated by the AIM2 inflammasome in the pathogenesis of EBI after SAH has not been clearly elucidated.
Hence, to better understand the mechanism of GSDMD-induced pyroptosis mediated by the AIM2 inflammasome in EBI following SAH, we used an in vivo mouse model of SAH and in vitro cellular model of SAH with oxyhaemoglobin (oxyHb). We also re-assessed GSDMD-induced pyroptosis in EBI following SAH after respectively interfering with the expression of AIM2 and caspase-1 with lentivirus (LV).
Discussion
In
the present study, we studied the possible role of GSDMD-induced
pyroptosis mediated by the AIM2 inflammasome in the pathogenesis of EBI
after SAH. The main findings can be summarised as follows: (1)
Pyroptosis-related proteins mediated by the AIM2 inflammasome were
upregulated in the brain temporal cortex after SAH and in primary
cortical neurons exposed to oxyHb. The expression levels of AIM2, GSDMD,
GSDMD-N, caspase-1, caspase-1 p20 and ASC increased continuously in a
time-dependent manner. (2) The results from the immunohistochemistry and
immunofluorescence staining showed that AIM2 inflammasome-mediated
pyroptosis mainly occurred in brain neurons. (3) The inhibition of AIM2
inflammasome activation by knocking down AIM2 and caspase-1 could
suppress GSDMD-induced neuronal pyroptosis by decreasing the expression
and activation of the pyroptosis-related proteins that are mediated by
the AIM2 inflammasome. (4) Knocking down caspase-1 suppressed not only
GSDMD activation-induced neuronal pyroptosis but also caspase-3
activation-induced neuronal apoptosis. These findings suggested, for the
first time, that pyroptosis could be involved in EBI after SAH through
the AIM2/Caspase-1/GSDMD pathway. Moreover, inhibiting the expression
and activation of caspase-1 could alleviate both pyroptosis and
apoptosis (Supplementary Figure).
The pathophysiology of SAH is complicated and involves multiple pathogenic mechanisms (e.g., inflammation, oxidative stress, and apoptosis). A growing body of evidence indicates that the inflammatory response plays a vital role in injury expansion and brain damage after SAH, including EBI, vasospasm, and delayed neurological deterioration2. In recent years, inflammasomes have been demonstrated to be important participants in EBI after SAH10. The inflammasome is a cytosolic multimeric signalling complex that responds to invading pathogens and host-derived danger signals such that its activation leads to caspase-1 activation. Inflammasome activation proceeds via the formation of a multimolecular complex containing a receptor, an adaptor such as ASC and the cysteine protease caspase-113. Then, activated caspase-1 triggers the maturation of the pro-inflammatory cytokines IL-1β and IL-18 and induces pyroptotic cell death. Several nucleotide-binding oligomerisation domain (NOD)-like receptors (NLRs), as well as AIM2-like receptors (ALRs), have been shown to form inflammasomes. Most of the inflammasomes described to date contain an NLR protein, namely, NOD-like receptor containing pyrin domain 1(NLRP1), NLRP2, NLRP3, NLRP6, NLRP7, NLRP12, and NLR- and caspase-activating recruitment domain-containing 4 (NLRC4). However, only a few inflammasomes have been studied in the CNS, namely, NLRP1, NLRP2, NLRP3 and AIM2. Among these inflammasomes, the NLRP3 inflammasome has been the most studied. NLRP3 inflammasome-mediated neuroinflammation is involved in many acute and chronic CNS diseases, including SAH10,14,15. In SAH, activation of the NLRP3 inflammasome is also essential for the modulation of pro-inflammatory cytokines, and inhibition of the NLRP3 inflammasome by pharmacological treatment can alleviate brain injury after SAH10,16.
In addition to NLRP3, AIM2 is also an important inflammasome involved in CNS infection and injury17. In the present study, we collected and analysed CSF samples from patients with or without SAH. The results from the analysis of patient-derived CSF samples revealed that the level of the AIM2 protein in the CSF of the SAH patients was significantly greater than that in the CSF from non-SAH patients. The higher the Hunt-Hess grade was, the higher the level of AIM2 that was found in the CSF. In the experimental SAH model, we also found that the AIM2 inflammasome was activated in vivo at 24 h post-SAH and that in vitro, the AIM2 inflammasome was significantly unregulated in cultured cortical neurons 6 h after incubation with oxyHb and the levels continued to increase for 12 and 72 h. To verify the role of GSDMD-induced pyroptosis mediated by the AIM2 inflammasome in EBI after SAH, LV was used to knock down the expression of AIM2. The results showed that AIM2 inflammasome-mediated pyroptosis was significantly alleviated in EBI following SAH.
As reported, the AIM2 inflammasome could be activated by aberrant dsDNA, including bacterial DNA and viral DNA, from pathogens and hosts and by endogenous self-DNA within the cytosol, damaged DNA within the nucleus, and self-DNA secreted by exosomes18. Wang et al. detected CSF DNA levels in patients with SAH and found that both nuclear and mitochondrial DNA levels in the CSF were significantly increased in the patients with SAH compared with volunteers, and the CSF nuclear and mitochondrial DNA levels were significantly higher on days 1 and 419. Moreover, higher CSF DNA levels were associated with worse outcomes for patients with SAH19. This result was consistent with the increased AIM2 in the SAH patients in our study. Combined with the results of this study showing that the level of AIM2 in CSF increased significantly within 3 days after SAH, we found that the elevated level of DNA in the CSF after SAH was synchronous and consistent with that of AIM2. Thus, we speculate that pyroptosis mediated by the AIM2 inflammasome is involved in EBI after SAH. This kind of EBI should be considered, to be exact, a secondary brain injury.
Recently, some scholars believe that pyroptosis should be redefined as GSDMD-mediated, rather than caspase-1-mediated, programmed necrosis20. GSDMD was discovered to form a pore and act as an effector for pyroptosis. In GSDMD-deficient cells, pyroptosis cannot be triggered by known canonical inflammasome ligands21. GSDMD contains ~480 amino acids in two domains, and the N-terminal gasdermin domain (GSDMD-N) and the C-terminal gasdermin domain (GSDMD-C) are linked by a long loop. Mounting evidence has demonstrated that GSDMD plays a key role in CNS injury22,23. In our study, we also observed that GSDMD was upregulated after SAH. Although GSDMD is considered the initiator of pyroptosis, GSDMD-N is the direct and sole effector of pyroptosis. Activated caspase-1 or caspase-11 efficiently cleaves GSDMD at a conserved glutamic acid residue (D276 in mouse and D275 in humans)21,24. The cleaved GSDMD unleashes the pro-pyroptotic N-terminal fragment from the auto-inhibited state maintained by the C-terminus, thus separating the role of GSDMD into that of GSDMD-N and that of GSDMD-C. The released GSDMD-N is oligomerized, and only the oligomerised form of GSDMD-N is able to translocate to the plasma membrane, where it induces cell rupture and the release of inflammatory cytokines, such as IL-1β25. We also observed that the GSDMD-N generated by caspase-1 cleavage forms an oligomer and migrates to the plasma membrane to kill cells.
Furthermore, GSDMD-N alone localises to the plasma membrane, as evidenced by GSDMD-N binding to liposomes in studies in vitro. Binding studies with liposomes and lipid strips revealed that GSDMD-N has a high affinity for liposomes containing lipids such as cardiolipin, phosphatidylinositol 4-phosphate [PI(4)P] and phosphatidylinositol 4,5-bisphosphate [PI(4,5)P] compared with other lipid types26. It is through its lipid-binding specificity that GSDMD-N disrupts plasma membranes, which it perpetrates only when exposed to the cytosolic PI-containing inner leaflet but not when exposed to the extracellular outer leaflet, which lacks PI26. While GSDMD-N kills from within the cell, its released form does not harm neighbouring cells. Mounting evidence has shown that the inner ring diameter of the pore formed by GSDMD-N is estimated to be between 10 and 20 nm6,27,28. Different methods have revealed a pore consisting of 16 or 24 GSDMD-N units27,28. This finding is consistent with the observation we made in the present study revealing that a large number of pore-like structures appear on the surface of neurons stimulated by oxyHb. The results of the membrane protein analysis suggest that the pore-like structure may be caused by the oligomerization of GSDMD-N at the cell membrane.
In the present study, we also interfered with the expression of caspase-1 by an LV. After caspase-1 was knocked down, GSDMD-induced pyroptosis was markedly reduced in EBI following SAH. Knocking down caspase-1 inhibited not only the expression and activation of GSDMD but also the expression of pyroptosis-related proteins mediated by the AIM2 inflammasome. We propose two explanations for this result: First, caspase-1-mediated inflammatory injury could be greatly alleviated after caspase-1 is knocked down. Caspase-1 is unequivocally required for the proteolytic processing of IL-1β and IL-18; these two cytokines engage their transmembrane receptors IL-1R and IL-18R to promote inflammation via the activation of nuclear factor-kappaB transcriptional programmes that are induced by the activation of myeloid differential protein-88, a key signalling adaptor29. When caspase-1 was knocked down, caspase-1-mediated inflammatory injury may have been alleviated, and the amount of dsDNA released from damaged cells could be reduced. Second, the non-functional AIM2/ASC complex was quickly depleted. Juruj et al. found that a negative feedback loop controlled by ASC/caspase-1 regulates AIM2 complex formation/stability13. In the absence of a functional AIM2 inflammasome, the AIM2/ASC complex formed very rapidly. However, this complex was then removed through activated autophagy following AIM2 speck formation13. Thus, when caspase-1 levels were deficient, the AIM2 inflammasome was not readily formed and pyroptosis was thus mediated after SAH.
Intriguingly, knocking down caspase-1 alleviated not only GSDMD activation-induced neuronal pyroptosis but also caspase-3 activation-induced neuronal apoptosis. A few other studies have reported that GSDMD-deficient cells may die because of the caspase-1 cleavage of caspase-3/721,30. Inhibiting caspase-1 activity may have attenuated caspase-3-dependent apoptosis, but the mechanism remains unclear31,32,33. We found that caspase-1 was essential for the activation of caspase-3. The cleavage of caspase-3 was significantly hindered when caspase-1 was knocked down in EBI following SAH. However, the expression of caspase-3 was not affected by caspase-1 knockdown. Therefore, we speculated that apoptosis was also alleviated in EBI after SAH, because knocking down caspase-1 hindered the cleavage of caspase-3. It was recently reported that GSDMD was also cleaved during apoptosis. GSDMD was cleaved by caspase-3/7 at D87 during apoptosis, while GSDMD was cleaved by caspase-1 at D275/D276 during pyroptosis34. The p30 N-terminal fragment of GSDMD (GSDMD p30) released by the cleavage at D275/D276 forms pores in the plasma membrane, thereby mediating pyroptotic cell death. Nevertheless, this cleaved GSDMD also generated the p43 fragment of GSDMD (GSDMD p43) at D87 during apoptosis, which inactivated or failed to trigger pyroptosis (Supplementary Figure). We preliminarily found that caspase-1 may be an important protein at the intersection of the pyroptosis and the apoptosis pathways. Inhibition of caspase-1 activity alleviated not only GSDMD activation-induced neuronal pyroptosis but also caspase-3 activation-induced neuronal apoptosis.
In this study, we demonstrated, for the first time, that the GSDMD-induced pyroptosis mediated by the AIM2 inflammasome may be involved in EBI after SAH. When inhibiting the activation of the AIM2 inflammasome by knocking down AIM2 and caspase-1 with LV, the pyroptosis mediated by the AIM2 inflammasome was significantly alleviated. The activation of caspase-3 was also decreased after caspase-1 was knocked down. However, a clearer regulatory mechanism between pyroptosis and apoptosis remains to be further explored.
The pathophysiology of SAH is complicated and involves multiple pathogenic mechanisms (e.g., inflammation, oxidative stress, and apoptosis). A growing body of evidence indicates that the inflammatory response plays a vital role in injury expansion and brain damage after SAH, including EBI, vasospasm, and delayed neurological deterioration2. In recent years, inflammasomes have been demonstrated to be important participants in EBI after SAH10. The inflammasome is a cytosolic multimeric signalling complex that responds to invading pathogens and host-derived danger signals such that its activation leads to caspase-1 activation. Inflammasome activation proceeds via the formation of a multimolecular complex containing a receptor, an adaptor such as ASC and the cysteine protease caspase-113. Then, activated caspase-1 triggers the maturation of the pro-inflammatory cytokines IL-1β and IL-18 and induces pyroptotic cell death. Several nucleotide-binding oligomerisation domain (NOD)-like receptors (NLRs), as well as AIM2-like receptors (ALRs), have been shown to form inflammasomes. Most of the inflammasomes described to date contain an NLR protein, namely, NOD-like receptor containing pyrin domain 1(NLRP1), NLRP2, NLRP3, NLRP6, NLRP7, NLRP12, and NLR- and caspase-activating recruitment domain-containing 4 (NLRC4). However, only a few inflammasomes have been studied in the CNS, namely, NLRP1, NLRP2, NLRP3 and AIM2. Among these inflammasomes, the NLRP3 inflammasome has been the most studied. NLRP3 inflammasome-mediated neuroinflammation is involved in many acute and chronic CNS diseases, including SAH10,14,15. In SAH, activation of the NLRP3 inflammasome is also essential for the modulation of pro-inflammatory cytokines, and inhibition of the NLRP3 inflammasome by pharmacological treatment can alleviate brain injury after SAH10,16.
In addition to NLRP3, AIM2 is also an important inflammasome involved in CNS infection and injury17. In the present study, we collected and analysed CSF samples from patients with or without SAH. The results from the analysis of patient-derived CSF samples revealed that the level of the AIM2 protein in the CSF of the SAH patients was significantly greater than that in the CSF from non-SAH patients. The higher the Hunt-Hess grade was, the higher the level of AIM2 that was found in the CSF. In the experimental SAH model, we also found that the AIM2 inflammasome was activated in vivo at 24 h post-SAH and that in vitro, the AIM2 inflammasome was significantly unregulated in cultured cortical neurons 6 h after incubation with oxyHb and the levels continued to increase for 12 and 72 h. To verify the role of GSDMD-induced pyroptosis mediated by the AIM2 inflammasome in EBI after SAH, LV was used to knock down the expression of AIM2. The results showed that AIM2 inflammasome-mediated pyroptosis was significantly alleviated in EBI following SAH.
As reported, the AIM2 inflammasome could be activated by aberrant dsDNA, including bacterial DNA and viral DNA, from pathogens and hosts and by endogenous self-DNA within the cytosol, damaged DNA within the nucleus, and self-DNA secreted by exosomes18. Wang et al. detected CSF DNA levels in patients with SAH and found that both nuclear and mitochondrial DNA levels in the CSF were significantly increased in the patients with SAH compared with volunteers, and the CSF nuclear and mitochondrial DNA levels were significantly higher on days 1 and 419. Moreover, higher CSF DNA levels were associated with worse outcomes for patients with SAH19. This result was consistent with the increased AIM2 in the SAH patients in our study. Combined with the results of this study showing that the level of AIM2 in CSF increased significantly within 3 days after SAH, we found that the elevated level of DNA in the CSF after SAH was synchronous and consistent with that of AIM2. Thus, we speculate that pyroptosis mediated by the AIM2 inflammasome is involved in EBI after SAH. This kind of EBI should be considered, to be exact, a secondary brain injury.
Recently, some scholars believe that pyroptosis should be redefined as GSDMD-mediated, rather than caspase-1-mediated, programmed necrosis20. GSDMD was discovered to form a pore and act as an effector for pyroptosis. In GSDMD-deficient cells, pyroptosis cannot be triggered by known canonical inflammasome ligands21. GSDMD contains ~480 amino acids in two domains, and the N-terminal gasdermin domain (GSDMD-N) and the C-terminal gasdermin domain (GSDMD-C) are linked by a long loop. Mounting evidence has demonstrated that GSDMD plays a key role in CNS injury22,23. In our study, we also observed that GSDMD was upregulated after SAH. Although GSDMD is considered the initiator of pyroptosis, GSDMD-N is the direct and sole effector of pyroptosis. Activated caspase-1 or caspase-11 efficiently cleaves GSDMD at a conserved glutamic acid residue (D276 in mouse and D275 in humans)21,24. The cleaved GSDMD unleashes the pro-pyroptotic N-terminal fragment from the auto-inhibited state maintained by the C-terminus, thus separating the role of GSDMD into that of GSDMD-N and that of GSDMD-C. The released GSDMD-N is oligomerized, and only the oligomerised form of GSDMD-N is able to translocate to the plasma membrane, where it induces cell rupture and the release of inflammatory cytokines, such as IL-1β25. We also observed that the GSDMD-N generated by caspase-1 cleavage forms an oligomer and migrates to the plasma membrane to kill cells.
Furthermore, GSDMD-N alone localises to the plasma membrane, as evidenced by GSDMD-N binding to liposomes in studies in vitro. Binding studies with liposomes and lipid strips revealed that GSDMD-N has a high affinity for liposomes containing lipids such as cardiolipin, phosphatidylinositol 4-phosphate [PI(4)P] and phosphatidylinositol 4,5-bisphosphate [PI(4,5)P] compared with other lipid types26. It is through its lipid-binding specificity that GSDMD-N disrupts plasma membranes, which it perpetrates only when exposed to the cytosolic PI-containing inner leaflet but not when exposed to the extracellular outer leaflet, which lacks PI26. While GSDMD-N kills from within the cell, its released form does not harm neighbouring cells. Mounting evidence has shown that the inner ring diameter of the pore formed by GSDMD-N is estimated to be between 10 and 20 nm6,27,28. Different methods have revealed a pore consisting of 16 or 24 GSDMD-N units27,28. This finding is consistent with the observation we made in the present study revealing that a large number of pore-like structures appear on the surface of neurons stimulated by oxyHb. The results of the membrane protein analysis suggest that the pore-like structure may be caused by the oligomerization of GSDMD-N at the cell membrane.
In the present study, we also interfered with the expression of caspase-1 by an LV. After caspase-1 was knocked down, GSDMD-induced pyroptosis was markedly reduced in EBI following SAH. Knocking down caspase-1 inhibited not only the expression and activation of GSDMD but also the expression of pyroptosis-related proteins mediated by the AIM2 inflammasome. We propose two explanations for this result: First, caspase-1-mediated inflammatory injury could be greatly alleviated after caspase-1 is knocked down. Caspase-1 is unequivocally required for the proteolytic processing of IL-1β and IL-18; these two cytokines engage their transmembrane receptors IL-1R and IL-18R to promote inflammation via the activation of nuclear factor-kappaB transcriptional programmes that are induced by the activation of myeloid differential protein-88, a key signalling adaptor29. When caspase-1 was knocked down, caspase-1-mediated inflammatory injury may have been alleviated, and the amount of dsDNA released from damaged cells could be reduced. Second, the non-functional AIM2/ASC complex was quickly depleted. Juruj et al. found that a negative feedback loop controlled by ASC/caspase-1 regulates AIM2 complex formation/stability13. In the absence of a functional AIM2 inflammasome, the AIM2/ASC complex formed very rapidly. However, this complex was then removed through activated autophagy following AIM2 speck formation13. Thus, when caspase-1 levels were deficient, the AIM2 inflammasome was not readily formed and pyroptosis was thus mediated after SAH.
Intriguingly, knocking down caspase-1 alleviated not only GSDMD activation-induced neuronal pyroptosis but also caspase-3 activation-induced neuronal apoptosis. A few other studies have reported that GSDMD-deficient cells may die because of the caspase-1 cleavage of caspase-3/721,30. Inhibiting caspase-1 activity may have attenuated caspase-3-dependent apoptosis, but the mechanism remains unclear31,32,33. We found that caspase-1 was essential for the activation of caspase-3. The cleavage of caspase-3 was significantly hindered when caspase-1 was knocked down in EBI following SAH. However, the expression of caspase-3 was not affected by caspase-1 knockdown. Therefore, we speculated that apoptosis was also alleviated in EBI after SAH, because knocking down caspase-1 hindered the cleavage of caspase-3. It was recently reported that GSDMD was also cleaved during apoptosis. GSDMD was cleaved by caspase-3/7 at D87 during apoptosis, while GSDMD was cleaved by caspase-1 at D275/D276 during pyroptosis34. The p30 N-terminal fragment of GSDMD (GSDMD p30) released by the cleavage at D275/D276 forms pores in the plasma membrane, thereby mediating pyroptotic cell death. Nevertheless, this cleaved GSDMD also generated the p43 fragment of GSDMD (GSDMD p43) at D87 during apoptosis, which inactivated or failed to trigger pyroptosis (Supplementary Figure). We preliminarily found that caspase-1 may be an important protein at the intersection of the pyroptosis and the apoptosis pathways. Inhibition of caspase-1 activity alleviated not only GSDMD activation-induced neuronal pyroptosis but also caspase-3 activation-induced neuronal apoptosis.
In this study, we demonstrated, for the first time, that the GSDMD-induced pyroptosis mediated by the AIM2 inflammasome may be involved in EBI after SAH. When inhibiting the activation of the AIM2 inflammasome by knocking down AIM2 and caspase-1 with LV, the pyroptosis mediated by the AIM2 inflammasome was significantly alleviated. The activation of caspase-3 was also decreased after caspase-1 was knocked down. However, a clearer regulatory mechanism between pyroptosis and apoptosis remains to be further explored.
